#include "bits/stdc++.h"

using namespace std;

typedef pair<int, int> P;
#define int long long
#define ll long long
#define mod 1000000007
#define INF (1LL<<60)

#define rep(i,n) for(int i=0, i##_len=(n); i<i##_len; ++i)




signed main(){

	int N;
	cin >> N;
	int a[100];

	a[1] = 1;
	a[2] = 2;
	for (int i = 3; i < 60; i++)
		a[i] = a[i - 1] + a[i - 2];

	cout << a[N] << endl;


	return 0;
}